Various types of patterns are formed on conductors, semiconductors, and insulators in all kinds of electronic equipment. There is a demand for higher pattern accuracy in pattern forming methods and pattern structural bodies. In particular, in pattern forming using printing, the number of processes is reduced compared with photolithography so lower costs can be expected, but forming fine patterns is an issue.
Pattern forming using printing is considered as a method of forming electronic devices at low cost. Printing methods include screen printing, gravure printing, inkjet printing, and the like, but it is difficult to form fine patterns with these printing methods as they are. Therefore, a method of forming fine patterns in which a lyophilic and lyophobic pattern is formed in advance so that the surface of the substrate to be printed has different wettability spatially, and clear pattern boundaries are obtained by printing thereupon with ink. For example, a method in which a surface is made hydrophilic by irradiating a hydrophobic organic layer with ultraviolet light via a photomask, and then, ink is formed on the hydrophilic portion by a dip method or a die coating method to form source and drain electrodes and the like of thin-film transistors is used as a method of forming a lyophilic and lyophobic pattern. Ultraviolet light with short wavelength of 150 to 350 nm may be used, and it is known that processing can be carried out in a short period of time by a combination of ultraviolet irradiation and ozone processing.
However, even though it is possible to adopt the methods of contacting the mask using ultraviolet light of wavelength shorter than 350 nm, it is difficult to combine with a projection optical system, and even if this was possible, there is a problem that the light exposure device would be extremely expensive. In addition, because the contact angle varies, the required light exposure processing time is increased (sensitivity is reduced), and apart from batch process with contact light exposure, it is difficult to process in a practical amount of time. The necessity for the exposure light to contact the mask means that with plastics for the substrate that deform, pattern alignment is difficult, so it is necessary to increase the design margin in accordance with the amount of deformation, so there is the problem that it is not possible to form patterns with high fineness (high degree of integration). Also, when ozone processing is combined with light irradiation, the contact angle at the interfaces of the pattern varies gently due to diffusion of the ozone, so there is a problem that it is not possible to form a fine pattern.
A method in which a hydrophobic layer is formed on a light absorbent layer, which is then irradiated with light so that the light absorbent layer generates heat, and the hydrophobic layer is decomposed to become hydrophilic by the heat energy has been proposed. Because heat is used, laser light which has high energy density must be used, and because of the heat, there is diffusion at the irradiation interfaces, so there is a problem that the interfaces between the lyophilic and lyophobic patterns are not sharp.